The Treasury Department sold $12.3 billion in three-month bills at an average discount rate of 5.17%, up from 5.15% last week. Another $12.3 billion was sold in six-month bills at an average rate of 5.23%, up from 5.20%. The three-month rate is the highest since the bills sold for 5.22% on April 28. The six-month bill rate is the highest since they averaged 5.26% on May 27. The new discount rates understate the actual return to investors: 5.31% for three-month bills, with a $10,000 bill selling for $9,869.30, and 5.45% for a six-month bill selling for $9,735.60. In a separate report, the Federal Reserve Board said the average yield for one-year Treasury bills rose to 5.55% last week from 5.48% the previous week. The next auction of 52-week bills will be Thursday; two-year notes, Aug. 26; five-year notes, Aug. 27.